1. Field of the Invention
The present invention relates to a ball screw feed mechanism in which, by rotating a ball screw around the axis thereof, a slider, which is screwed with the ball screw, is made to slide in the axial direction of the ball screw.
2. Description of the Related Art
Technology (a printing plate automatic exposure device) has been developed in which, by using a printing plate (hereinafter xe2x80x9cphotopolymer platexe2x80x9d) in which a photosensitive layer (e.g., a photopolymerizable layer) is provided on a support, an image is recorded by a direct laser beam or the like onto the photopolymerizable layer of the photopolymer plate.
In such a technology, photopolymer plates are taken out one-by-one from a magazine which accommodates a plurality of photopolymer plates, and the photopolymer plates are supplied to an exposure section where the aforementioned recording is carried out. Directly before the exposure section, the photopolymer plate is placed on a basically smooth and flat surface plate and is positioned on the surface plate. Thereafter, the photopolymer plate is fed out together with the surface plate to the exposure section.
An example of the driving mechanism for moving the surface plate is a driving mechanism including a ball screw whose axial direction is along the moving direction of the surface plate and which rotates around its own axis due to driving force of a motor; a slider which is integrally connected to the surface plate and which is screwed together with the ball screw; and a guide rod which is disposed parallel to the ball screw, passes through the slider, and guides the slider in the axial direction of the ball screw. In this driving mechanism, by rotating the ball screw, the slider is slid while being guided by the guide rod, and the surface plate slides together with the slider. Further, in the exposure section, exposure is carried out basically in accordance with the amount of rotation of the ball screw.
However, by operating the motor which rotates the ball screw, the motor itself vibrates. This vibration may be transferred to the ball screw, such that the ball screw vibrates. Here, if the vibration frequency of the motor coincides with the resonance frequency of the ball screw or the bearings and the like supporting the ball screw, the vibration of the ball screw, and thus the vibration of the surface plate, becomes large, such that irregularities arise in the image formed on the photopolymer plate.
In view of the aforementioned, an object of the present invention is to provide a ball screw feed mechanism in which vibration of a ball screw is reduced.
A first aspect of the ball screw feed mechanism of the present invention includes: a ball screw which is rod-shaped, and at whose outer peripheral portion a male screw is formed, and which rotates around a shaft of the ball screw due to driving force of a driving device; a slider which is screwed together with the ball screw, and which slides along an axial direction of the ball screw due to rotation of the ball screw around the axis of the ball screw; a supporting portion which supports the ball screw at an axial direction end portion of the ball screw such that the ball screw is displaceable along the axial direction of the ball screw; and an urging device which urges the ball screw in a direction opposite to a displacement direction, with respect to displacement of the ball screw along the axial direction of the ball screw.
In the ball screw feed mechanism of the above-described structure, the ball screw receives driving force of the driving device and rotates, and the slider is thereby slid along the axial direction of the ball screw. When various types of vibration, such as vibration of the driving device caused by its own driving force, are generated, the vibration may be transmitted to the ball screw such that the ball screw vibrates in its own axial direction. Here, even in a case in which the resonance frequency of the ball screw itself coincides with the frequency of the aforementioned vibration due to the material, the configuration or the like of the ball screw, in the present ball screw feed mechanism, when the ball screw is displaced in accordance with the vibration along the axial direction, the urging device urges the ball screw in the direction opposite to this displacement in an attempt to forcibly return the ball screw to its original position. In this way, the resonance point is forcibly shifted. The vibration of the ball screw is thereby mitigated, and accordingly, the vibration of the slider is reduced.
A second aspect of the present invention is a ball screw feed mechanism including: a ball screw which is rod-shaped, and at whose outer peripheral portion a male screw is formed, and which rotates around a shaft of the ball screw due to driving force of a driving device; a slider which is screwed together with the ball screw, and which slides along an axial direction of the ball screw due to rotation of the ball screw around the axis of the ball screw; a supporting portion which supports the ball screw at an axial direction end portion of the ball screw such that the ball screw is displaceable along a direction orthogonal to the axial direction of the ball screw; and an urging device which urges the ball screw in a direction opposite to a displacement direction, with respect to displacement of the ball screw along the direction orthogonal to the axial direction of the ball screw.
In the ball screw feed mechanism of the above-described structure, the ball screw receives driving force of the driving device and rotates, and the slider is thereby slid along the axial direction of the ball screw. When various types of vibration, such as vibration of the driving device caused by its own driving force, are generated, the vibration may be transmitted to the ball screw such that the ball screw vibrates in a direction orthogonal to its own axial direction (i.e., in the rotary radial direction of the ball screw). Here, even in a case in which the resonance frequency of the ball screw itself coincides with the frequency of the aforementioned vibration due to the material, the configuration or the like of the ball screw, in the present ball screw feed mechanism, when the ball screw is displaced in accordance with the vibration along the direction orthogonal to the axial direction, the urging device urges the ball screw in the direction opposite to this displacement in an attempt to forcibly return the ball screw to its original position. In this way, the resonance point is forcibly shifted. The vibration of the ball screw is thereby mitigated, and accordingly, the vibration of the slider is reduced.
A third aspect of the present invention is a method for reducing vibration in a ball screw feed mechanism, wherein the ball screw feed mechanism includes a slider threadably disposed on a rod, with the slider moving along the rod when the rod rotates, the method comprising: (a) extending one end of the rod through a bearing; (b) applying urging forces along three different directions to the bearing, with each direction being substantially orthogonal to each of the other directions, for resisting displacements of the rod; and (c) rotatably driving the rod using a motor to apply rotational mechanical energy to the end of the rod extending through the bearing.